WO 2006/116764 published Nov. 2, 2006 to Shionogi & Co. Ltd of Osaka, Japan teaches various polycyclic carbamoylpyridone compounds having HIV integrase activity. At page 113, there is described a reaction sequence as follows:
whereby selenium dioxide is added to a solution of the benzyl ether of maltol designated above as (ii), heating the mixture to 160° C., recovering aldehyde (c) and then oxidizing the aldehyde with sodium chlorate to yield carboxylic acid (ci).